It’s the 24th century, and you’re a curator at the Starfleet Museum of Ancient Technology. Archaeologists have unearthed a “TV tube,” an ancient device for displaying moving images. Your job is to get it working. One reference says the device accelerated electrons, which then bombarded a screen to produce images; to the electrons, the tube was 57 cm long. You measure the tube and find it’s 60 cm long. To get it working, you need to know the electrons’ speed and the potential difference needed to accelerate them. The electron’s rest energy is 511 keV.